The present invention relates to magnetic solenoids and, more particularly, to rotary solenoids in which a permanent magnet is utilized to maintain the armature in an actuated, moved or latched configuration.
A typical rotary latching solenoid includes an electric energizing coil mounted within a housing or case, a base attached to the case and having a pole face, an armature which is rotatably mounted on the case and includes a hub extending through the case and a pole face facing the base pole face, a spring return for returning the armature to an unlatched position, and a latching mechanism which holds the armature in a latched or closed position against the return torque of the spring. In one such device, disclosed in U.S. Pat. No. 4,470,030 to Myers, the latching mechanism employs a permanent magnet which is mounted on the case opposite the base. When the coil of the solenoid is energized, a flux flow path extends about the coil and through the armature hub and base. The flux lines pass across the pole faces of the armature and base and draw the armature toward the base pole face.
The Myers' device includes an inclined ball race which converts the linear forces developed by the coil to rotary motion, thereby causing the armature to rotate relative to the base, and against a return spring, to an energized position. When in this position, the pole faces of the armature and hub and base are sufficiently close to allow the flux of the permanent magnet to flow between the armature and base when the coil is deenergized, thereby maintaining the armature in the energized position.
The armature is released to its deenergized position by pulsing the coil with the current in a reverse direction, thereby temporarily cancelling the magnet holding flux created and allowing the spring return to rotate the armature in the opposite direction to the initial rest position.
Although such rotary latching solenoids are compact and efficient, there are some disadvantages with their construction. For example, in the aforementioned Myers' device, the permanent magent is positioned immediately adjacent to the inclined ball race mechanism, so that the flux of the permanent magnet flows through the ball race mechanism. The magnetization of the ball races make them susceptible to accumulation of metal filings or other magnetic particles, which can result in fouling of the ball race mechanism.
Another disadvantage of such latching solenoids is that the pole faces of the armature and base are in a plane perpendicular to the axis of rotation of the solenoid. Since the inclined ball race mechanism is sloped at a relatively slight inclination, a relatively large radial rotation causes only relatively small displacement of the armature pole face away from the base pole face. Accordingly, the flux or holding force of the permanent magnet must be relatively strong in order to counteract this return movement of the armature, as caused by the inclined ball races.
Accordingly, there is a need for a latching solenoid in which the susceptibility of the ball races to contamination by magnetic particles is minimized. Furthermore, there is a need for a latching solenoid in which the armature and base design make a more efficient use of the flux from the permanent magnet when the armature is rotated to a latched position.